(a) Field of the Invention
The invention relates to new paclitaxel derivatives showing an increased solubility in water.
(b) Description of Prior Art
Paclitaxel is a natural product extracted from the bark of the Pacific yew (Taxus brevifolia). It was thereafter found in other members of the Taxacae family including the yew of Canada (Taxus canadensis) found in Gaspesia, eastern Canada and Taxus baccata found in Europe whose needles contain paclitaxel and analogs and hence provide a renewable source of paclitaxel and derivatives. The crude extract was tested for the first time during the 60s and its active principle was isolated in 1971 by Wani et al. who at the same time identified its chemical structure. It showed a wide range of activity over melanoma cells, leukemia, various carcinomas, sarcomas and non-Hodgkin lymphomas as well as a number of solid tumors in animals. Clinical studies show that paclitaxel is a promising anti cancer agent. Paclitaxel is a microtubule blocker, but unlike other drugs inhibiting the mitosis by interaction with microtubules such as colchicin, vincristin and podophyllotoxin, paclitaxel does not prevent tubulin assembly. It rather accelerates the tubulin polymerization and stabilizes the assembled microtubules. The drug acts in a unique way which consists in binding to microtubules, preventing their depolymerization under conditions where usually depolymerization occurred (dilution, calcium, cold and microtubules disrupting drugs). Paclitaxel blocks the cell cycle at prophase which results in an accumulation of cells in G2+M. Because of its unique structure and mechanism of action, paclitaxel was submitted to clinical trials. Interesting activity against many tumors, especially breast cancer and ovarian cancer refractory to chemotherapy, has been observed. However, because of its poor solubility in water, the product had to be administered in ethanol, Cremophor-EL and 5% sucrose diluted in saline or water. Cremophor-EL was responsible for hypersensitivity reactions observed in several patients (Rowinsky, E. K., et al., J. Nat. Can. Inst., 82 (15), 1247-1259). Premedication with anti-histamines had to be administered in order to reduce the toxicity.
Poor solubility of paclitaxel constitutes an important limitation to its administration to cancer patients. To increase paclitaxel availability, total and partial synthesis have been reported. The improvement of paclitaxel solubility was obtained by adjunction of solubilizing functions such as carbonyl or sulfonyl groups with good results. Some of the synthesized products were more active than paclitaxel, many others had a biological activity equivalent or slightly inferior to that of paclitaxel while being far more soluble in water (KINGSTON, D. G., Pharmacol. Ther. (England), 52(1) p1-34, 1991). The complexity of the paclitaxel chemical structure rendered its total synthesis very difficult until recently when it was achieved simultaneously by two different groups. However the yield of this synthesis of the order of 2-4% will have little impact on the paclitaxel availability (BORMAN, S., Total synthesis of anticancer agent paclitaxel was achieved by two different routes (C@EN. February, 32-34, 1994)).
Many attempts have been made to improve paclitaxel aqueous solubility with various components resulting in poorly stable products or inactive ones. Moreover, sometimes the synthesis of these compounds required many chemical steps.
Paclitaxel has three hydroxyl groups at carbon 1, 7 and 2' susceptible of undergoing an acylation. Their reactivity varies according to the following order: 2'&gt;7&gt;&gt;&gt;1 (MATHEW, A. E., et al., J. Med. Chem., 35, 145-151, 1992). Acylation on 2'C is the best way of paclitaxel modification because of its great reactivity, and because even if 2' acylpaclitaxels loose their property of promoting the microtubules polymerization in vitro, they are hydrolyzed in the cell and revert to paclitaxel and keep their cytotoxic activity (KINGSTON, D. G., et al., J. Nat. Prod., 1-13, 1990; and MELLADO, W., et al., Biochem. Biophys. Res. Commun., 105, 1082-1089, 1984).
Accordingly, to increase solubility, several derivatives have been synthesized by modification of the 2' or/and 7 hydroxyls. The 2' hydroxyl appears as a good candidate for chemical modification. The 7 hydroxyl requires more drastic conditions to react while the tertiary hydroxyl in position 1 is inert. The 2' and 7 hydroxyls have been modified with several groups (Deutsch, H. M., et al., J. Med. Chem., 32, 788-792, 1989; Rose, W. C., et al., Cancer Chemother. Pharmacol., 39, 486, 1997) but only a few derivatives were synthesized with a sugar moiety as reported by Kingston et al. (Kingston, D. G. I., Pharmac. Ther., 52, 1-34, 1991). However, many derivatives were insufficiently soluble, inactive or too unstable to be applied in a clinical situation.
It would be highly desirable to be provided with new active paclitaxel derivatives having improved solubility with respect to paclitaxel.
It would be highly desirable to be provided with a simple, rapid and accurate immunological method for the measurement of paclitaxel in biological fluids and in Taxus crude extracts.
It would be highly desirable to be provided with a fluorescent derivative of paclitaxel, which binds to microtubules, to discriminate apoptotic cells.